Q: "When did Burnside finally revert back to command of IX Corps and not Right Wing?"
According to F.H. Dyer, Compendium of the War of the Rebellion, vol. 1, p. 313, Burnside gave place to Reno as Ninth Corps commander on Sept. 3, Burnside assuming command of McClellan's right wing. After his death at Fox's Gap Reno was succeeded in turn by Cox 9/14, Willcox 10/8, Sedgwick 1/16/63, W.F. Smith 2/5/63. Burnside then resumed corps command on 3/17/63. Technically speaking, McClellan's wing system remained in place until Burnside assumed army command in early November '62. Burnside then converted McClellan's wings into grand divisions.
This progression could be laboriously confirmed in ORs.
Also, Burnside having but one corps (Ninth) to his right wing, after Hooker's First was withdrawn, is no breach of campaign practice. Franklin commanded the left wing in like fashion with one corps (Sixth) augmented by Couch's division of Fourth Corps which was not officially assigned to Sixth until after Antietam. Confusing isn't it.
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